Fiber optic cables are widely used in the communications industry. For indoor and outdoor applications these cables are generally provided in loose tube and tight buffer cable construction types. Loose tube cables contain one or more optical fibers within one or more loose tubes. Excess fiber length is provided within the loose tube allowing fiber movement during flexure and tensile loading. In tight buffer cables, each individual optical fiber is contained under a thermoplastic sheath applied directly to the fiber protective coating. This thermoplastic tight buffer sheath provides added protection for each fiber for crush and impact forces during handling and installation.
In addition to increased protection for crush and impact forces, tight buffer cables provide protection from moisture exposure when constructed from suitable outdoor rated materials. However, these cables contain more material than loose tubes because each fiber has an individual buffer. This additional material causes the cables to have large diameters, particularly for high fiber counts, resulting in lower fiber density and higher costs.
Loose tube cables provide high density of fibers in a compact construction, especially if the fibers are contained in ribbons. However, loose tubes have low inherent resistance to crush or impact forces and moisture exposure, so the cable must be rated for low exposure levels or protections must be provided elsewhere in the cable design. Also, fiber ribbons have a preferential bend axis which may limit the ability of the cable to perform in sharp bends without twisting.
If multiple fibers are provided in a small loose tube fiber unit design, an even more compact and higher density cable can be constructed. However, these fiber unit loose tube cables are not well suited for indoor and outdoor applications and are not designed for direct termination to multi-fiber connectors.